2. Field of the Invention
This application refers to fuel compositions particularly useful in internal combustion engines and more particularly useful in spark ignition engines.
With the advent of automobile engines that require the use of non-leaded gasolines (to prevent disablement of catalytic converters used to reduce undesirable emissions), a serious problem has arisen in providing gasoline of high enough octane to prevent knocking and the concomitant damage which it causes. The chief problem lies in the area of the degree of octane requirement increase, herein called "ORI", which is caused by deposits formed in the combustion chamber while the engine is operating on commercial gasolines.
The basis of the ORI problem is as follows: each engine, when new, requires a certain minimum octane fuel in order to operate satisfactorily without pinging and/or knocking. As the engine is operated on any gasoline, this minimum octane increases and, in most cases, if the engine is operated on the same fuel for a prolonged period will reach equilibrium. This is apparently caused by an amount of deposits in the combustion chamber. Equilibrium is typically reached after 5000 to 15,000 miles of automobile operation.
Octane requirement increases at equilibrium with commercial gasolines, in particular engines will vary from 5 or 6 octane units to as high as 12 or 13 units, depending upon the gasoline compositions and engine design. The seriousness of the problem is thus apparent. A typical 1975 or 1976 automobile with an octane requirement of 85 may after a few months of operation require 97 octane gasoline for proper operation, and little unleaded gasoline of that octane is available. The ORI problem exists in some degree with engines operated on leaded fuels. U.S. Pat. Nos. 3,144,311 and 3,146,203 disclose lead-containing fuel compositions having reduced ORI properties.
It is, however, believed by many experts that the ORI problem, while present with leaded gasolines, is much more serious with unleaded fuel because of the different nature of the deposits formed with the respective fuels, and because of the lesser availability of high-octane non-leaded fuels. This problem is compounded by the fact that the most common means of enhancing the octane of unleaded gasoline, increasing its aromatic content, also appears to increase the octane requirement of the engine.
It is thus highly desirable to provide lead-free fuel compositions which moderate the octane requirement increases achieved when operated in typical modern automotive engines.
2. Description of the Prior Art
U.S. Pat. No. 2,706,077 discloses gasoline compositions containing lower dialkyl formamides, particularly dimethyl and diethyl formamide, as antistalling additives. Only dimethyl formamide was tested and claimed.
U.S. Pat. No. 2,918,359 discloses gasolines containing a synergistic antistalling composition comprising a lower N,N-disubstituted formamide and a lower alkanol. The formamides are disclosed as having from 1- to 7-carbon alkyl groups; N,N-diethyl, N,N-di-N-propyl, N,N-diisopropyl and N-methyl-N-ethyl are specifically disclosed. Only gasolines containing the combination of dimethyl formamide and isopropanol were tested and claimed.